1. Technical Field
The embodiments described herein are related to Radio Frequency Identification (RFID) systems and more particularly to methods and apparatus to prevent unwanted and/or unwarranted access to information stored on an RFID chip.
2. Related Art
RFID is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. The technology requires some extent of cooperation of an RFID reader and an RFID tag. An RFID tag is an object that can be applied to or incorporated into a variety of products, packaging, identification mechanisms, etc., for the purpose of identification and tracking using radio waves. For example, RFID is used in enterprise supply chain management to improve the efficiency of inventory tracking and management. Some tags can be read from several meters away and beyond the line of sight of the reader.
Most RFID tags contain at least two parts: One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and transmitting the signal. As the name implies, RFID tags are often used to store an identifier that can be used to identify the item to which the tag is attached or incorporated. But in today's systems, a RFID tag can contain non-volatile, possibly writable, e.g., EEPROM for storing additional data as well.
Most RFID systems use a modulation technique known as backscatter to enable the tags to communicate with the reader or interrogator. In a backscatter system, the interrogator transmits a Radio Frequency (RF) carrier signal that is reflected by the RFID tag. In order to communicate data back to the interrogator, the tag alternately reflects the RF carrier signal in a pattern understood by the interrogator. In certain systems, the tag can include its own carrier generation circuitry to generate a signal that can be modulated with data to be transmitted to the interrogator.
RFID tags come in one of three types: passive, active, and semi passive. Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming RF signal from the interrogator provides just enough power for the, e.g., CMOS integrated circuit in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier wave from the reader. This means that the antenna has to be designed both to collect power from the incoming signal and also to transmit the outbound backscatter signal.
Passive tags have practical read distances ranging from about 10 cm (4 in.) (ISO 14443) up to a few meters (Electronic Product Code (EPC) and ISO 18000-6), depending on the chosen radio frequency and antenna design/size. The lack of an onboard power supply means that the device can be quite small. For example, commercially available products exist that can be embedded in a sticker, or under the skin in the case of low frequency RFID tags.
Unlike passive RFID tags, active RFID tags have their own internal power source, which is used to power the integrated circuits and to broadcast the response signal to the reader. Communications from active tags to readers is typically much more reliable, i.e., fewer errors, than from passive tags.
Active tags, due to their on board power supply, also may transmit at higher power levels than passive tags, allowing them to be more robust in “RF challenged” environments, such as environments with humidity; with dampening targets, including humans/cattle, which contain mostly water; reflective targets such as metal, shipping containers, vehicles, etc.; or at longer distances. In turn, active tags are generally bigger, caused by battery volume, and more expensive to manufacture, caused by battery price.
Many active tags today have operational ranges of hundreds of meters, and a battery life of up to 10 years. Active tags can include larger memories than passive tags, and may include the ability to store additional information received from the reader, although this is also possible with passive tags.
Semi-passive tags are similar to active tags in that they have their own power source, but the battery only powers the microchip and does not power the broadcasting of a signal. The response is usually powered by means of backscattering the RF energy from the reader, where energy is reflected back to the reader as with passive tags. An additional application for the battery is to power data storage.
The battery-assisted reception circuitry of semi-passive tags leads to greater sensitivity than passive tags, typically 100 times more. The enhanced sensitivity can be leveraged as increased range, by one magnitude, and/or as enhanced read reliability, by reducing bit error rate at least one magnitude.
The enhanced sensitivity of semi-passive tags place higher demands on the interrogator concerning separation in more dense population of tags. Because an already weak signal is backscattered to the reader from a larger number of tags and from longer distances, the separation requires more sophisticated anti-collision concepts, better signal processing and some more intelligent assessment of which tag might be where.
FIG. 1 is a diagram illustrating an exemplary RFID system 100. In system 100, RFID interrogator 102 communicates with one or more RFID tags 110. Data can be exchanged between interrogator 102 and RFID tag 110 via radio transmit signal 108 and radio receive signal 112. RFID interrogator 102 comprises RF transceiver 104, which contains transmitter and receiver electronics, and antenna 106, which are configured to generate and receive radio transit signal 108 and radio receive signal 112, respectively. Exchange of data can be accomplished via electromagnetic or electrostatic coupling in the RF spectrum in combination with various modulation and encoding schemes.
RFID tag 110 is a transponder that can be attached to an object of interest and act as an information storage mechanism. In many applications, the use of passive RFID tags is desirable, because they have a virtually unlimited operational lifetime and can be smaller, lighter, and cheaper than active RFID tags that contain an internal power source, e.g. battery. Passive RFID tags power themselves by rectifying the RF signal emitted by the RF scanner. Consequently, the range of transmit signal 108 determines the operational range of RFID tag 110.
RF transceiver 104 transmits RF signals to RFID tag 110, and receives RF signals from RFID tag 110, via antenna 106. The data in transmit signal 108 and receive signal 112 can be contained in one or more bits for the purpose of providing identification and other information relevant to the particular RFID tag application. When RFID tag 110 passes within the range of the radio frequency electromagnetic field emitted by antenna 106, RFID tag 110 is excited and transmits data back to RF interrogator 102. A change in the impedance of RFID tag 110 can be used to signal the data to RF interrogator 102 via receive signal 112. The impedance change in RFID tag 110 can be caused by producing a short circuit across the tag's antenna connections (not shown) in bursts of very short duration. RF transceiver 104 senses the impedance change as a change in the level of reflected or backscattered energy arriving at antenna 106.
Digital electronics 114, which can comprise a microprocessor with RAM, performs decoding and reading of receive signal 112. Similarly, digital electronics 114 performs the coding of transmit signal 108. Thus, RF interrogator 102 facilitates the reading or writing of data to RFID tags, e.g. RFID tag 110 that are within range of the RF field emitted by antenna 104. Together, RF transceiver 104 and digital electronics 114 comprise reader 118. Finally, digital electronics 114 and can be interfaced with an integral display and/or provide a parallel or serial communications interface to a host computer or industrial controller, e.g. host computer 116.
Today, RFID tags are being incorporated into sensitive documents and identification devices such as passports; travel cards, e.g., the travel card being introduced under the Western Hemisphere Travel Initiative (WHTI); driver's licenses; etc. Most of the RFID protocols in use today do not require a password or other authentication/verification scheme to read information from an RFID tag. Since some of these tags can be read at more than 20 ft, any reader operating at the same frequency and using the same protocol as the tag can read the tag's information. Moreover, there are no methods presently to detect an unauthorized reading of the tag, so the user would have no idea their information has been read. This is major concern for privacy of the individual or the object which is being tagged.